Introduction

Islamic State of Iraq and Syria (ISIS), a predominantly Sunni jihadist group, seeks to sow civil unrest in Iraq and the Levant with the aim of establishing a caliphate—a single, transnational Islamic state based on sharia. The group emerged in the ashes of the U.S.-led invasion to oust Saddam Hussein as al-Qaeda in Iraq (AQI), and the insurgency that followed provided it with fertile ground to wage a guerrilla war against coalition forces and their domestic allies.

After a U.S. counterterrorism campaign and Sunni efforts to maintain local security in what was known as the Tribal Awakening, AQI violence diminished from its peak in 2006–2007. But since the withdrawal of U.S. forces in late 2011, the group has increased attacks on mainly Shiite targets in what is seen as an attempt to reignite conflict between Iraq's Sunni minority and the Shiite-dominated government of Prime Minister Nouri al-Maliki. Burgeoning violence in 2013 left nearly eight thousand civilians dead, making it Iraq's bloodiest year since 2008, according to the United Nations. Meanwhile, in 2012 the group adopted its new moniker, ISIS (sometimes translated as Islamic State of Iraq and the Levant, or ISIL) as an expression of its broadened ambitions as its fighters have crossed into neighboring Syria to challenge both the Assad regime and secular and Islamist opposition groups there. By June 2014, the group's fighters had routed the Iraqi military in the major cities of Fallujah and Mosul and established territorial control and administrative structures on both sides of the Iraqi-Syrian border.

Origins

The insurgent group was launched by Abu Musab al-Zarqawi, an Arab of Jordanian descent, and flourished in the sectarian tensions that followed the U.S.-led invasion of Iraq in 2003. Zarqawi had commanded volunteers in Herat, Afghanistan, before fleeing to northern Iraq in 2001. There he joined with Ansar al-Islam (Partisans of Islam), a militant Kurdish separatist movement, for whom he led the group's Arab contingent. Analysts say this group, not al-Qaeda, was the precursor to AQI.

Ahead of the 2003 invasion, U.S. officials made a case before the UN Security Council linking Zarqawi's group with Osama bin Laden, though some experts say it wasn't until October 2004 that Zarqawi vowed obedience to the al-Qaeda leader. The U.S. State Department designated AQI a foreign terrorist organization that same month. "For al-Qaeda, attaching its name to Zarqawi's activities enabled it to maintain relevance even as its core forces were destroyed [in Afghanistan] or on the run," wrote Brian Fishman, a counterterrorism fellow at the New America Foundation.

According to a 2011 report by the Center for Strategic and International Studies, Zarqawi developed a four-pronged strategy [PDF] to defeat the coalition: isolate U.S. forces by targeting its allies; discourage Iraqi collaboration by targeting government infrastructure and personnel; target reconstruction efforts through high-profile attacks on civilian contractors and aid workers; and draw the U.S. military into a Sunni-Shiite civil war by targeting Shiites.

The Coalition Provisional Authority (CPA), the transitional government established by the United States and its coalition partners, made two decisions early in the U.S.-led occupation that are often cited as having fed the insurgency. The CPA's first order banned members of Saddam Hussein's Ba'ath party from government positions (so-called "de-Baathification"); its second order disbanded the Iraqi army and security services, creating hundreds of thousands of new coalition enemies, many of them armed Sunnis.

"For al-Qaeda, attaching its name to Zarqawi's activities enabled it to maintain relevance even as its core forces were destroyed [in Afghanistan] or on the run." —Brian Fishman, New America Foundation

AQI's fighters were drawn initially from Zarqawi's networks [PDF] in Pakistan and Afghanistan, and later merged with recruits from Syria, Iraq, and its neighbors. The group's makeup became predominantly Iraqi by 2006, the Washington Post reported. But while the group peaked in 2006 and 2007 at the height of Iraq's sectarian civil war—which AQI helped foment—its ranks were diminished by a counterterrorism campaign by U.S. Special Operations Forces and the U.S.-backed Sahwa, or Sunni Awakening movement.

Leadership

Osama bin Laden and Zawahiri believed AQI's indiscriminate attacks on fellow Muslims would erode public support for al-Qaeda in the region, and in July 2005 they questioned Zarqawi's strategy in written correspondence. Fishman said the relationship collapsed when Zarqawi ignored al-Qaeda instructions to stop attacking Shiite cultural sites.

A U.S. air strike that killed Zarqawi in June 2006 marked a victory for U.S. and Iraqi intelligence and a turning point for AQI. In its aftermath, Abu Ayyub al-Masri, an Egyptian-born explosives expert and former Zawahiri confidant, emerged as AQI's new leader. In October 2006, Masri adopted the alias Islamic State of Iraq (ISI) to increase the group's local appeal, which suffered just as Zawahiri had feared, and embody its territorial ambitions; it later came to be known as ISIS, reflecting its broadened ambitions as instability in neighboring Syria after the 2011 uprising there created new opportunities to exploit.

ISIS is currently led by Abu Bakr al-Baghdadi, also known as Abu Du'a. The U.S. government believes he resides in Syria.

Funding

Supporters in the region, including those based in Jordan, Syria, and Saudi Arabia, are believed to have provided the bulk of past funding. Iran has also financed AQI, crossing sectarian lines, as Tehran saw an opportunity to challenge the U.S. military presence in the region, according to the U.S. Treasury and documents confiscated in 2006 from Iranian Revolutionary Guards operatives in northern Iraq. In early 2014, Iran offered to join the United States in offering aid to the Iraqi government to counter al-Qaeda gains in Anbar province.

The bulk of ISIS's financing, experts say, comes from sources such as smuggling, extortion, and other crime. ISIS has relied in recent years on funding and manpower from internal recruits [PDF]. Even prior to ISIS's takeover of Mosul, Iraq's second-largest city, in June 2014, the group extorted taxes from businesses small and large, netting upwards of $8 million a month, according to some estimates.

Staying Power

Heavy-handed actions taken by Maliki to consolidate power in the wake of the U.S. withdrawal have alienated much of the Sunni minority, and ISIS has since exploited the "failed social contract," said former CFR press fellow Ned Parker. Maliki's Shiite-dominated government was reluctant to integrate Awakening militias into the national security forces, and critics say he has persecuted Sunni political rivals and stoked sectarian polarization for political gain.

Sunnis who felt marginalized by the Maliki government began protesting for reforms in Anbar province in December 2012, and prominent Shiite clerics such as the Grand Ayatollah Ali Sistani and Moqtada al-Sadr acknowledged the legitimacy of their grievances, Parker wrote. According to a report by the nonpartisan Congressional Research Service [PDF], there were roughly a dozen days in 2012 on which ISIS executed multi-city attacks that killed at least twenty-five Iraqis. On at least four of those days, coordinated attacks left more than a hundred Iraqis dead.

In April 2013, Iraqi security forces raided a protest camp at al-Hawijah, provoking an escalation in Sunni militancy. Car bombings and suicide attacks intensified, with coordinated attacks regularly targeting Shiite markets, cafes, and mosques. In 2013, 7,818 civilians (including police) were killed in acts of terrorism and violence, more than double the 2012 death toll, according to United Nations figures. An additional 17,891 were injured, making 2013 Iraq's bloodiest year since 2008. At the end of 2013, security forces sought to clear a protest camp in Ramadi. The move provoked an uprising in which security forces pulled out of the city as well as nearby Fallujah, and ISIS moved to fill the void.

Meanwhile, the civil war in neighboring Syria has drawn Sunni jihadists into the rebellion against the regime of Bashar al-Assad, which is dominated by the Alawite sect, an offshoot of Shiite Islam.

While al-Qaeda-linked groups in Syria have fought among themselves and with the secular opposition, the Free Syrian Army signed a truce with ISIS in late September, an acknowledgment of their efficacy on the battlefield. But divisions within the Islamist opposition camp remain stark.

ISIS declared a merger with Jabhat al-Nusra, an al-Qaeda affiliate that has greater indigenous legitimacy in Syria, in April 2013. But Zawahiri, who succeeded bin Laden as head of so-called "core al-Qaeda," annulled the merger, ruling that Baghdadi's group's operations be limited to Iraq. Baghdadi rejected Zawahiri's ruling and questioned his authority, his group's pledge of fealty to al-Qaeda notwithstanding. Various rival Islamist militant groups coalesced in late 2013 as the Mujahedeen Army with the common goal of forcing ISIS to cede territory and leave Syria.

At odds with al-Qaeda's aims, ISIS has since expanded its territorial control, establishing a "de facto state in the borderlands of Syria and Iraq" that exhibits some of the traditional markers of sovereignty, note Douglas A. Ollivant and Fishman. Beyond fielding a militia, it provides limited services and administers its ultraconservative brand of justice. Much of Anbar province has remained outside the central government's authority since January 2014, and in mid-2014, a Sunni insurgency wrested control of Mosul and its environs after the predominantly Shiite army, hobbled by desertions and cronyism, retreated overnight. ISIS is at the vanguard of the insurgency, but the tactical alliances it has formed with non-jihadi Sunnis, including former members of the Ba'athist regime, have led analysts and policymakers to question how long it can rule over a population concerned by ISIS's extremism.

The takeovers highlighted Baghdad's weakness: In Fallujah, Maliki called on Sunni tribesmen to resist ISIS, and in Mosul, which had been considered a model for the surge and Awakening, he called on the Kurdish security forces, the peshmerga, to do the same. Maliki has also mobilized Shiite militias implicated in sectarian killings, and Iraqi forces are accused of indiscriminate airstrikes. Meanwhile, ISIS gains in the country's north set back the peshmerga and have created a humanitarian crisis for thousands of Iraqi Christians and Yezidis, who are among religious and ethnic minorities targeted by ISIS.

Insurgents' consolidation of territorial control is a concern for the United States, which believes such areas outside of state authority may become safe havens for those jihadis with ambitions oriented toward the "far enemy"—the West. The Obama administration has responded to the regional resurgence by increasing the CIA's support for the Maliki government, including assistance to elite counterterrorism units that report directly to the prime minister, and providing Hellfire missiles and surveillance drones. After Iraqi forces retreated from Mosul, the insurgents who routed them released more than one thousand prisoners and picked up troves of U.S.-supplied matériel.

Additional Resources

The International Crisis Group explains how Prime Minister Nouri al-Maliki's policies have benefitted al-Qaeda in Iraq as it took control of parts of Anbar province.

Will McCants describes factions within al-Qaeda, including the ISIS–al-Nusra internecine conflict.

Rania Abouzeid reports on the backlash against ISIS among rebel groups in Syria.

The New York Times presents a visual guide to the 2014 crisis in Iraq.